The present application relates to media delivery, and more particularly to media multicasting by integrating scalable overlay peer-to-peer tree networks with IP multicasting.
Background: Media Streaming
With the development of general broadband network access, there has been increasing interest in media streaming systems, methods, devices and protocols. Peer-to-peer (“P2P”) media streaming systems have been developed to overcome limitations in traditional server-based streaming. In a P2P media distribution system, cooperative peers may self-organize themselves into an overlay network via unicast tunnels. The peers cache and relay data for receipt by other peers, eliminating the need for powerful centralized servers to provide data to each and every client.
Some typical overlays used in P2P media streaming are tree structure overlays and a gossip mesh. The tree structure builds one or more overlay trees to distribute data among nodes. Examples include application-layer multicast (“ALM”) schemes (e.g., Narada and NICE) and some P2P video-on-demand systems (e.g., P2Cast and P2VoD).
A gossip mesh is built among nodes using gossip algorithms, with nodes exchanging data with their neighbors in the mesh. While a gossip mesh typically enjoys better resilience regarding network and group dynamics, gossip-based approaches typically suffer from a higher control overhead due to data scheduling and mesh maintenance. A gossip mesh may have poor playback delay as the data clips are transmitted over multiple paths to a node and the length of the paths create video delay.
Trees introduce lower end-to-end delay and are typically easier to maintain. Some previously proposed tree-based ALM protocols such as Narada, NICE, DT, Scribe, ALMI, etc.) assume that none of the routers are multicast-capable and hence have not considered the use of the underlying multicast capability.
Although global IP multicast is not available today, many local networks in today's Internet include multicasting. These local multicast-capable domains, or so-called “islands,” are often interconnected by multicast-incapable or multicast-disabled routers.
What is needed, therefore, is an ALM system that makes use of the local multicast capabilities in building trees.
Most ALM protocols only make use of unicast transmission. They move the multicast-related functionalities from routers to nodes and achieve multicast via piece-wise unicast connections. ALM works without the need of multicast routers. However, it is not as efficient as IP multicast. More packets have to be transmitted in the network and users have to suffer larger delay before the packets are received.
Though protocols such as Scattercast, YOID, UMTP, mTunnel, AMT, UniversalMulticast (UM) and Subset Multicast (SM) have been proposed to combine IP multicast with ALM, many of them require special nodes, such as proxies or routers.
Others require manual configuration for inter-node connections. Some have proposed a distributed approach to integrate IP multicast and ALM where each island has a designated leader. The leader identifies some ingress and egress nodes in its island for data delivery. This approach puts heavy control loads on leaders and has complex mechanism for the in of leaders, ingress nodes, and egress nodes.
Scalable Island Multicast for Peer-to-Peer Media Delivery
SIM has integrated IP multicast with ALM to achieve higher transmission efficiency. This integration is especially important for streaming applications. Define link stress as the number of copies of a packet transmitted over a certain physical link. We have done simulations to evaluate some representative ALM protocols. In a group of 1024 hosts, protocols such as Narada, GNP-based DT, TAG, Overcast achieve average link stresses of 2.9, 2.69, 2.61 and 2.02, respectively. The maximum link stresses achieved by these protocols are 40, 24, 28 and 14, respectively. Considering that a single stream usually requires several hundred Kbps transmission rate, the current Internet often cannot provide enough bandwidth for the streaming. On the other hand, as IP multicast always keeps the stresses of all the delivery links being 1, it significantly improves the delivery efficiency and reduces the bandwidth consumption. Therefore. SIM is more applicable for streaming applications than pure ALM protocols.
The advantages of the proposed approach are highlighted as follows:                A fully distributed scheme that combines IP multicast with ALM for media streaming. No central control or management is needed. The system is hence scalable to a large number of users.        Fully autonomous. A host can automatically detect multicast island to join. It does not require any special nodes (such as special routers or proxies) and does not need any manual configuration.        Low control overhead. Hosts are divided into two multicast groups (a CONTROL group and a DATA group) and multicast control messages are transmitted only in the CONTROL group. Hosts not in the CONTROL group will not receive any control messages. Furthermore, each island only needs one ingress host. There are no overheads to select leaders or egress hosts.        